a network of permanent and temporary conduits (canals and pipes) that supply water to irrigated lands from an irrigation source; a key element of an irrigation system. A network consists of conduit and regulation networks and is equipped with devices and structures to measure the water (water-measuring flumes), to raise its level in the canals and regulate discharge (main and runoff regulators), to interconnect canals (cascades and chutes), and to retain sediment (sedimentation ponds and guide systems).
In open irrigation systems the conduit network consists of the main canal and interfarm and intrafarm distribution canals of various levels. The main canal supplies water from a river, reservoir, well, or other source to the interfarm distribution canals, which supply it to the separate farms or crop-rotation sectors; the intrafarm distribution canals deliver water to the fields of the rotation or to irrigation sectors. In some cases the supply network does not have a full complement of canals. The irrigation canals are arranged in such a way as to minimize construction and operation costs while providing for the supply of water in the required quantities and at the required times, as well as maximum canal efficiency (the ratio of water discharge at the end of the canal to discharge at the beginning). Other goals are to maximize the land-use ratio of the irrigated areas and to provide for efficient operation of the canals and structures on such areas. An essential condition for the operation of an irrigation network is that the main canal have a water level higher than that of canals of lower ranks and that higher-ranking canals be higher than lower-ranking canals so that the water flows by gravity.
The routes of irrigation canals should pass along the boundaries of farms, crop-rotation sectors, and fields, so that the irrigated area is not dissected, and the main canal must pass along the highest points of the irrigated area. The canals are set in excavations or banked semiexcavations or on slopes of hills. To reduce water losses to seepage, the bottom and sides of canals are compacted or covered with cast or prefabricated concrete or reinforced concrete; screens of clay and polymeric films are also used, and reinforced-concrete chute canals are built.
In closed irrigation systems the supply network consists of a main pipeline, which feeds water from the source into the distribution pipes, which are laid at a depth of 0.6–1.2 m (sometimes on the surface). The required pressure is provided by the slope of the terrain or by a pumping station. In addition to complete absence of seepage losses, a closed irrigation network makes possible automation of the distribution of water over the irrigated area, and also increases the efficiency of land use and does not interfere with the operation of farm machinery. It is particularly efficient in systems with mechanized water-lifting and in cases of complex terrain.
The regulation network in open irrigation systems consists of temporary irrigation canals and field ridges from which the water enters the irrigation network (ridges and strips) or is taken up by sprinklers and irrigation machines. A regulation network is cut each year before irrigation begins and is leveled afterward or before each watering and during each postirrigation cultivation.
In closed irrigation systems the temporary irrigation canals and field ridges are usually replaced by underground pipes, portable irrigation hoses (with outlets into each ridge), or sectional pipelines with hydrants to feed water to sprinklers and irrigation machines.
REFERENCESKostiakov, A. N. Osnovy melioratsii, 6th ed. Moscow, 1960.
Popov, K. V. Meliorativnye kanaly. Moscow, 1969.
Korshikov, A. A. Ustroistvo vremennoi orositel’noi i polivnoi seti. Moscow, 1971.
N. G. RAEVSKAIA